According to
this History of Microbiology website, the famous biologist Anton van
Leeuwenhoek first discovered Amoeba:
"1670's ------------------ Anton van Leeuwenhoek lived in the Netherlands
and was the owner of a dry goods business. He had a natural curiosity for
examining things that could not be seen with the naked eye. He observed
hair fibers, skin scaled, eye lenses, blood cells, feces and sperm cells.
He documented his findings and submitted a letter to the Royal Society of
London with detailed drawings of what he saw. He discovered
Animalcules, tiny micro organisms in pond water today known as
Paramecium and Amoeba."